Cap structure coupled to source to reduce saturation current in hemt device

ABSTRACT

In some embodiments, the present disclosure relates to a high voltage device that includes a substrate comprising a first semiconductor material. A channel layer that comprises a second semiconductor material is arranged over the substrate. An active layer that comprises a third semiconductor material is arranged over the channel layer. Over the active layer is a source contact spaced apart from a drain contact. A gate structure is arranged laterally between the source and drain contacts and over the active layer to define a high electron mobility transistor (HEMT) device. Between the gate structure and the source contact is a cap structure, which is coupled to the source contact and laterally spaced from the gate structure. The cap structure and a gate electrode of the gate structure comprise a same material.

BACKGROUND

Modern day integrated chips comprise millions or billions ofsemiconductor devices formed on a semiconductor substrate (e.g.,silicon). Integrated chips (ICs) may use many different types oftransistor devices, depending on an application of an IC. In recentyears, the increasing market for cellular and RF (radio frequency)devices has resulted in a significant increase in the use of highvoltage transistor devices. For example, high voltage transistor devicesare often used in power amplifiers in RF transmission/receiving chainsdue to their ability to handle high breakdown voltages (e.g., greaterthan about 50V) and high frequencies. High electron mobility transistor(HEMT) devices are one promising candidate for high voltage transistordevices that operate at high frequencies with fast switching speeds andlow noise.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A, 1B and 1C illustrate a cross-sectional view, a top-view and aperspective view of some embodiments of a high electron mobilitytransistor (HEMT) device comprising a cap structure that continuouslyextends along a length of a source contact.

FIGS. 2A, 2B and 2C illustrate a cross-sectional view, a top-view and aperspective view of some embodiments of a HEMT device comprising a capstructure that has multiple cap segments spaced apart from one anotherand extending along a length of a source contact.

FIGS. 3-17 illustrate cross-sectional views of some embodiments of amethod of forming a HEMT device having a cap structure contacting asource contact.

FIG. 18 illustrates a flow diagram of the method illustrated in FIGS.3-17.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

A high electron mobility transistor (HEMT) device includes aheterojunction which is at an interface between two materials havingdifferent band gaps and which acts as a channel region of the HEMT. Forexample, the heterojunction is disposed over a semiconductor substrateand can be disposed between a gallium nitride layer and an aluminumgallium nitride layer. Further, a gate electrode is arranged over theheterojunction and between a source contact and a drain contact tocontrol current flow between the source and drain contacts of the HEMT.

During operation of the HEMT device, when a suitable voltage bias isapplied across the gate electrode and the source and drain contacts, acurrent flows along the heterojunction. The applied voltage biascontrols if the HEMT device operates in an enhancement mode or adepletion mode. In the enhancement mode, the HEMT device uses a gate tosource voltage to switch the HEMT device “ON” (e.g., to “turn on”current between source and drain). Thus, in enhancement mode, the HEMTdevice is a “normally open” switch in some regards. In depletion mode,the HEMT device uses a gate to source voltage to switch the device “OFF”(e.g., to “turn off” current between source and drain). Thus, indepletion mode, the HEMT device is a “normally closed” switch in someregards.

In the enhancement mode, the current at the heterojunction eventuallyreaches a saturation current which is the maximum current that can flowalong the heterojunction before breakdown. In high voltage applications,in the enhancement mode, the saturation current may become too large,which, in some embodiments, may cause device failure by, for example,local heating in the HEMT device.

The present disclosure, in some embodiments, relates to a cap structureon a HEMT device that directly contacts the source contact and thatcomprises a same material as the gate electrode. The cap structure isarranged laterally between the gate electrode and the source contact andis spaced from the gate electrode. The cap structure is biased accordingto the source contact and puts the channel region into a partiallydepleted mode. Thus, when the HEMT device is in the enhancement mode,the cap structure partially depletes the channel region (e.g., partially“turns off” current between source and drain) and the saturation currentis reduced. As a result, during high voltage applications, the HEMTdevice with the cap structure has a reduced saturation current anddevice failure is mitigated.

FIG. 1A illustrates a cross-sectional view 100A of some embodiments of aHEMT device comprising a cap structure coupled to a source contact.

The HEMT device includes a channel layer 104 over a substrate 102. Anactive layer 108 is arranged over the channel layer 104. The activelayer 108 and the channel layer 104 meet at an interface known as aheterojunction 124 that is substantially parallel or co-planar to a topsurface of the substrate 102. In some embodiments, the channel layer 104comprises a binary III/V semiconductor (e.g., a first III-nitridematerial like gallium nitride or gallium arsenide) and the active layer108 comprises a ternary III/V semiconductor (e.g., a second III-nitridematerial like aluminum gallium nitride or aluminum gallium arsenide). Insome embodiments, an isolation structure 106 surrounds outer sidewallsof the active layer 108 and upper portions of the channel layer 104. Asource contact 116 and a drain contact 110 are arranged over the activelayer 108. In some embodiments, the source contact 116 and the draincontact 110 directly contact the active layer 108. The source contact116 and the drain contact 110 are laterally spaced apart from oneanother. Laterally between the source contact 116 and the drain contact110 is a gate electrode 112 over a gate barrier layer 114. In someembodiments, the drain contact 110, the source contact 116, and the gateelectrode 112 are spaced apart from one another by a passivation layer122. In other embodiments, the drain contact 110, the source contact116, and the gate electrode 112 are spaced apart from one another by apassivation layer 122 and also a dielectric structure 126. Contact vias120 that are embedded in the dielectric structure 126 are coupled to thedrain contact 110, the source contact 116, and the gate electrode 112.

In some embodiments, a cap structure 118 is arranged over the activelayer 108 and coupled to the source contact 116. In some embodiments,the cap structure 118 comprises a horizontally extending portion 118 hand a vertically extending portion 118 v. The horizontal direction maybe parallel to an upper surface of the substrate 102, whereas thevertical direction may be normal to the upper surface of the substrate102 and thus, perpendicular to the horizontal direction. Thehorizontally extending portion 118 h of the cap structure 118 directlycontacts a sidewall of the source contact 116. The horizontallyextending portion 118 h, in some embodiments, is spaced apart from theactive layer 108 by the passivation layer 122. In some embodiments, atleast a lower region of the vertically extending portion 118 v of thecap structure 118 is spaced apart from the source contact 116 by thepassivation layer 122. In some embodiments, an upper region of thevertically extending portion 118 v of the cap structure 118 contacts thehorizontally extending portion 118 h of the cap structure 118. In someembodiments, a lower surface of the vertically extending portion 118 vdirectly contacts the active layer 108. Thus, in some embodiments, thecap structure 118 resembles an “L” shape. In such embodiments, the capstructure 118 may resemble the “L” shape due to manufacturing techniques(see, method in FIGS. 3-17).

The cap structure 118 comprises a same material as the gate electrode112. For example, in some embodiments, the cap structure 118 and thegate electrode 112 may comprise titanium nitride, nickel, tungsten,titanium, or platinum. The cap structure 118 and the gate electrode 112comprise a different material than the source contact 116. For example,in some embodiments, the source contact 116 may comprise titanium oraluminum. In some embodiments, the cap structure 118 comprises a firstmaterial that has a higher work function than the active layer 108 suchthat the cap structure 118 is coupled to the active layer 108 as aSchottky contact, whereas the source contact 116 comprises a secondmaterial different from the first material that has a lower workfunction than the active layer 108 such that the source contact 116 iscoupled to the active layer 108 as an Ohmic contact. The cap structure118 is electrically coupled to the source contact 116 to receive a samevoltage bias that the source contact 116 receives. By being coupled tothe source contact 116 and by acting as a Schottky contact, the capstructure 118 partially depletes the channel region along theheterojunction 124 and thus, reduces the saturation current of the HEMTdevice when in the enhancement mode (e.g., when the HEMT device is“ON”). As a result, the cap structure 118 increases the reliability ofthe HEMT device when operating at high voltages.

FIG. 1B illustrates a top-view 100B of some embodiments of a HEMT devicecomprising a cap structure coupled to a source contact.

In some embodiments, the top-view 100B of FIG. 1B corresponds to thecross-sectional view 100A of FIG. 1A, except that the passivation layer122, the dielectric structure 126, and the contact vias 120 are notillustrated in the top-view 100B. In some embodiments, the isolationstructure 106 is continuously connected in a rectangular, ring-likeshape and completely surrounds the active layer 108. In someembodiments, the source contact 116 is spaced from the gate electrode112 by a fourth width w₄ and the drain contact 110 is spaced from thegate electrode 112 by a sixth width w₆. In some embodiments, the sixthwidth w₆ is greater than the fourth width w₄. For example, in someembodiments, the fourth width w₄ may be in range of betweenapproximately 1.1 micrometers and approximately 2 micrometers. Forexample, in some embodiments, the sixth width w₆ is greater than thefourth width w₄. In some embodiments, the sixth width w₆ may be equal toapproximately 23 micrometers. The source contact 116 has a first widthw₁ that is substantially uniform along its length. The drain contact 110has a seventh width w₇ that is substantially uniform along its length.In some embodiments, the first width w₁ and the seventh width w₇ are thesame. For example, in some embodiments, the first width w₁ and theseventh width w₇ may each be equal to approximately 1 micrometer. Also,in some embodiments, the source contact 116 and the drain contact 110comprise a same, conductive material. The gate electrode 112 has a fifthwidth w₅ that is substantially uniform along its length. In someembodiments, the fifth width w₅ is greater than the first width w₁ andthe seventh width w₇. For example, in some embodiments, the fifth widthw₅ may be equal to approximately 1.4 micrometers.

The cap structure 118 has a second width w₂ that corresponds to thewidth of the horizontally extending portion 118 h of the cap structure118 and a third width w₃ that corresponds to the vertically extendingportion 118 v of the cap structure 118. The sum of the second and thirdwidths, w₂+w₃, indicates the width of the cap structure 118 from thetop-view 100B perspective and is the maximum width of the cap structure118, whereas, the third width w₃ indicates a minimum width of the capstructure 118. In some embodiments, the second width w₂ and the thirdwidth w₃ may be the same. In other embodiments, the second width w₂ maybe less than or greater than the third width w₃. In some embodiments,the sum of the second and third widths, w₂+w₃, may be in a range ofbetween approximately 0.1 micrometers and approximately 1 micrometer. Inother embodiments, the minimum value of third width w₃ and the minimumvalue of the second width w₂ may each be at least, for example,approximately 0.5 micrometers. Thus, the cap structure 118 may add up to1 micrometer to the total width (w₁+w₄+w₅+w₆+w₇) of the HEMT device. Insome embodiments, the total width (w₁+w₄+w₅−Fw₆+w₇) of the HEMT devicemay be in a range of between approximately 27.5 micrometers andapproximately 28.4 micrometers. The second and/or third widths w₂, w₃may be extended to adjust the desired saturation current of the HEMTdevice.

FIG. 1C illustrates a perspective view 100C of some embodiments of aHEMT device comprising a cap structure coupled to a source contact.

In some embodiments, the perspective view 100C of FIG. 1C corresponds tothe cross-sectional view 100A of FIG. 1A, except that the passivationlayer 122, the dielectric structure 126, and the contact vias 120 arenot illustrated in the perspective view 100C. The perspective view 100Cmay also correspond to the top-view 100B of FIG. 1B. In someembodiments, the source contact 116, the drain contact 110 and the gateelectrode 112 are spaced from the isolation structure 106. For example,in some embodiments, a first sidewall 110 f of the drain contact 110 anda second sidewall 110 s of the drain contact 110 may directly overliethe active layer 108. In other embodiments (not shown), at least someportions of the source contact 116 and/or the drain contact 110 directlyoverlie at least some portions of the isolation structure 106. Forexample, in such other embodiments, the first sidewall 110 f of thedrain contact 110 may directly overlie the isolation structure 106, andthe second sidewall 110 s of the drain contact 110 may directly overliethe active layer 108. Further, in some embodiments, a top surface of theisolation structure 106 is substantially co-planar with a top surface ofthe active layer 108. In some embodiments, the cap structure 118 has atop surface that is substantially co-planar with a top surface of thesource contact 116. The source contact 116 has a first length L₁, andthe cap structure 118 has a second length L₂, wherein the first andsecond lengths L₁, L₂ are measured in a direction that is perpendicularto the measurement direction of the widths illustrated in FIG. 1B. Insome embodiments, the cap structure 118 continuously extends along thefirst length L₁ of the source contact 116, such that the first length L₁and the second length L₂ are equal.

In some embodiments, the cap structure 118 may reduce the saturationcurrent by more than 50 percent when the HEMT device is in enhancementmode. For example, in some embodiments, when the cap structure 118 ispresent, when the voltage bias across the source contact 116 and thedrain contact 110 is equal to 6 volts and when a voltage bias applied tothe drain contact 110 is equal to 20 volts, the saturation current ofthe HEMT device is approximately 2 amperes. In contrast, if the sameaforementioned conditions are applied to the source contact 116, thedrain contact 110, and the gate electrode 112, but the cap structure 118is not present, the saturation current of the HEMT device isapproximately 5 amperes. Thus, in this example, the presence of the capstructure 118 reduces the saturation current of the HEMT device by 60percent. Further, in some embodiments, under high voltage applications,when the cap structure 118 is present, the HEMT device can withstand avoltage bias applied to the drain contact 110 of up to 450 volts withoutbreakdown. In contrast, in other embodiments where the cap structure 118is not present, the HEMT device can only withstand a voltage biasapplied to the drain contact 110 of up to 300 volts without breakdown.Thus, the presence of the cap structure 118 greatly reduces thesaturation current of a HEMT device to allow for high voltageapplications without device failure.

FIG. 2A illustrates a cross-sectional view 200A of some alternativeembodiments of a HEMT device comprising a cap structure coupled to asource contact.

The cross-sectional view 200A of FIG. 2A comprises the same elements asthe cross-sectional view 100A of FIG. 1A. However, the cross-sectionalview 200A of FIG. 2A, although identical to the cross-sectional view100A of FIG. 1A, may correspond to a cap structure 118 with differentfeatures.

FIG. 2B illustrates a top-view 200B of some alternative embodiments of aHEMT device comprising a cap structure coupled to a source contact.

In some embodiments, the top-view 200B of FIG. 2B corresponds to thecross-sectional view 200A of FIG. 2A, except that the passivation layer122, the dielectric structure 126, and the contact vias 120 are notillustrated in the top-view 100B. The top-view 200B of FIG. 2B comprisesthe same features as the top-view 100B of FIG. 1B, except that the capstructure 118 comprises multiple cap segments 118 s. Each cap segment118 s is spaced from a nearest neighbor by a first distance di. In someembodiments, the minimum value of the first distance di may be, forexample, approximately 0.5 micrometers. In some embodiments, from thetop-view 200B perspective, the multiple cap segments 118 s of the capstructure 118 cover approximately 5% to approximately 10% less of aregion of the active layer 108 compared to the cap structure 118 of FIG.1B that continuously extends along the length of the source contact 116and covers 100% of the region of the active layer 108. In someembodiments, the second width w₂, the third width w₃, and/or the firstdistance di of the cap structure 118 with multiple cap segments 118 smay be increased or decreased to adjust the desired saturation currentof the HEMT device, which provides more flexibility in designing areliable HEMT device compared to the cap structure 118 that continuouslyextends along the length of the source contact 116 in FIG. 1B.

FIG. 2C illustrates a perspective view 200C of some embodiments of aHEMT device comprising a cap structure coupled to a source contact.

In some embodiments, the perspective view 200C of FIG. 2C corresponds tothe cross-sectional view 200A of FIG. 2A, except that the passivationlayer 122, the dielectric structure 126, and the contact vias 120 arenot illustrated in the perspective view 200C. The perspective view 200Cmay also correspond to the top-view 200B of FIG. 2B. In the perspectiveview 200C, the cap structure 118 comprises 9 cap segments 118 s. It willbe appreciated that the cap structure 118 may comprise any number of capsegments 118 s, and that the 9 cap segments 118 s in FIG. 3C isarbitrary. In some embodiments, top surfaces of the cap segments 118 sare substantially co-planar with a top surface of the source contact116. Each cap segment 118 s directly contacts and is electricallycoupled to the source contact 116. Thus, each cap segment 118 s receivesthe same voltage bias as the source contact 116 through the contact via(120 of FIG. 2A) that is coupled to the source contact 116.

FIGS. 3-17 illustrate cross-sectional views 300-1700 of some embodimentsof a method of forming a HEMT device comprising a cap structure coupledto a source contact. Although FIGS. 3-17 are described in relation to amethod, it will be appreciated that the structures disclosed in FIGS.3-17 are not limited to such a method, but instead may stand alone asstructures independent of the method.

As shown in the cross-sectional view 300 of FIG. 3, a substrate 102comprising a first semiconductor material having a first doping type(e.g., p-type or n-type) is provided. In some embodiments, the substrate102 comprises p-type silicon, which is a widely available substrate andtherefore reduces cost of the HEMT device. A channel layer 104 isdeposited over the substrate 102. The channel layer 104 comprises asecond semiconductor material that is different than the firstsemiconductor material. An active layer 108 comprising a thirdsemiconductor material is deposited over the channel layer 104. In someembodiments, the channel layer 104 comprises a binary III/Vsemiconductor whereas the active layer 108 comprises a ternary III/Vsemiconductor. For example, in some embodiments, the channel layer 104may comprise gallium nitride (GaN) and the active layer 108 may comprisealuminum gallium nitride (AlGaN). In other embodiments, the channellayer 104 may comprise gallium arsenide (GaAs) and the active layer 108may comprise aluminum gallium arsenide (AlGaAs). In some embodiments,the channel layer 104 and/or the active layer 108 may be formed over thesubstrate 102 by a deposition process (e.g., chemical vapor deposition(CVD), plasma enhanced chemical vapor deposition (PE-CVD), atomic layerdeposition (ALD), physical vapor deposition (PVD), etc.). In someembodiments, an isolation structure (106 of FIG. 1A) may be formed tosurround the active layer 108 and partially surround the channel layer104. At an interface between the active layer 108 and the channel layer104 is a heterojunction 124, which may act as a channel region when avoltage bias is present. The heterojunction 124 may be present because,in part, the second semiconductor material of the channel layer 104 hasa different band gap than the third semiconductor material of the activelayer 108. For example, aluminum gallium nitride (AlGaN) has a largerband gap than gallium nitride (GaN).

As shown in the cross-sectional view 400 of FIG. 4, in some embodiments,a barrier material 414 may be deposited over the active layer 108. Thebarrier material 414, in some embodiments, may comprise the secondsemiconductor material having a second doping type (e.g., p-type). Forexample, in some embodiments, the barrier material 414 may comprisep-doped gallium nitride (p-GaN). In other embodiments, the barriermaterial 414 may comprise a dielectric material (e.g., an oxide, anitride, or the like). Thus, like the channel layer 104, the barriermaterial 414 may be formed over the active layer 108 by a depositionprocess (e.g., chemical vapor deposition (CVD), plasma enhanced chemicalvapor deposition (PE-CVD), atomic layer deposition (ALD), physical vapordeposition (PVD), etc.).

As shown in the cross-sectional view 500 of FIG. 5, the barrier material414 of FIG. 4 may be patterned to form a gate barrier layer 114. Thegate barrier layer 114 may be formed by photolithography and etchingsteps. The gate barrier layer 114 is formed on an area of the activelayer 108 that is meant for a gate electrode.

As shown in the cross-sectional view 600 of FIG. 6, a conformalpassivation layer 602 is deposited over the active layer 108. Theconformal passivation layer 602 may comprise, in some embodiments anitride or an oxide, such as, for example, silicon nitride, siliconoxynitride, silicon oxide, or the like.

As shown in the cross-sectional view 700 of FIG. 7, a source/drain mask702 is formed over the conformal passivation layer 602. Usingphotolithography and an etch (e.g., a dry etch) that is selective to theconformal passivation layer 602 and the source/drain mask 702, thesource/drain mask 702 and the conformal passivation layer 602 arepatterned to define a source cavity 706 and a drain cavity 704. Thesource cavity 706 and the drain cavity 704 have bottom surfaces definedby the active layer 108.

As shown in the cross-sectional view 800 of FIG. 8, a source contact 116and a drain contact 110 are formed within the source cavity (706 of FIG.7) and the drain cavity (704 of FIG. 7), respectively. In someembodiments, the source and drain contacts 116, 110 may be formed bydepositing a conductive layer over the source/drain mask (702 of FIG. 7)to fill the source and drain cavities (706, 704 of FIG. 7), performing aplanarization process (e.g., chemical mechanical planarization) suchthat the conductive layer is co-planar with the source/drain mask (702of FIG. 7), and then removing the source/drain mask (702 of FIG. 7),such that the remaining conductive layer defines the source contact 116and the drain contact 110. Thus, in some embodiments, the source contact116 comprises a same material as the drain contact 110. For example, insome embodiments, the source contact 116 and the drain contact 110 maycomprise titanium or aluminum. In some embodiments, the material of thesource contact 116 and the drain contact 110 has a work function that isless than the work function of the active layer 108 such that the sourceand drain contacts 116, 110 act as Ohmic contacts with the active layer108. Further, in some embodiments, the formation of the source and draincontacts 116, 110 may include a heating process to promote the materialof the source and drain contacts 116, 110 to diffuse into the activelayer 108 and increase the Ohmic behavior of the source and draincontacts 116, 110. In some embodiments, the source contact 116 has a topsurface that is above a top surface of a region of the conformalpassivation layer 602 that contacts the source contact 116. Similarly,in some embodiments, the drain contact 110 has a top surface that isabove a top surface of a region of the conformal passivation layer 602that contacts the drain contact 110. In some embodiments, the topsurfaces of the source contact 116 and the drain contact 110 may besubstantially co-planar due to the planarization process.

As shown in the cross-sectional view 900A of FIG. 9A, a first patterningstep is performed to remove portions of the conformal passivation layer(602 of FIG. 8) to define a cap cavity 902 and a gate cavity 904. Thefirst patterning step may be performed by depositing a photoresist,patterning the photoresist using a mask structure and photolithography,performing an etch according to the patterned photoresist, and removingthe patterned photoresist. The mask structure is designed such that thepatterned photoresist acts as a mask to define the cap cavity 902 andthe gate cavity 904 in the passivation layer 122. In some embodiments, afirst portion 906 of the passivation layer 122 separates the cap cavity902 from the source contact 116, and a second portion 908 of thepassivation layer 122 separates the cap cavity 902 from the gate cavity904. In some embodiments, the gate cavity 904 has a width that is lessthan the width of the gate barrier layer 114. In other embodiments, thegate cavity 904 may be substantially aligned with outermost sidewalls ofthe gate barrier layer 114.

The top-view 900B in FIG. 9B corresponds to some embodiments of thecross-sectional view 900A of FIG. 9A. As shown in the top-view 900B, insome embodiments, the cap cavity 902 is spaced from the source contact116 along a first direction, wherein the first direction is parallel toa top surface of the substrate (102 of FIG. 3). The cap cavity 902exposes the active layer 108, and the gate cavity 904 exposes the gatebarrier layer 114. In some embodiments, the cap cavity 902 continuouslyextends along a length of the source contact 116, wherein the length ofthe source contact 116 is measured in a second direction that isperpendicular to the first direction and parallel to the top surface ofthe substrate (102 of FIG. 3). In some embodiments, the gate cavity 904is arranged closer to the source contact 116 than to the drain contact110.

The top-view 900C in FIG. 9C corresponds to some embodiments of thetop-view 900B of FIG. 9B. As shown in the top-view 900C, in someembodiments, the cap cavity 902 comprises multiple cap cavity segments902 s. Each cap cavity segment 902 s is spaced apart from a nearestneighbor by a first distance di in the first direction and is spacedapart from the source contact 116 in the second direction. The capcavity segments 902 s are substantially aligned to one another along thefirst direction. Compared to the cap cavity 902 in FIG. 9C comprisingmultiple cap cavity segments 902 s, the cap cavity 902 in FIG. 9B thatcontinuously extends along the length of the source contact 116 may beformed with a simpler mask structure.

As shown in the cross-sectional view 1000 of FIG. 10, a masking layer1002 is deposited over the passivation layer 122 and within the capcavity (902 of FIG. 9A) and the gate cavity (904 of FIG. 9A). In someembodiments, the masking layer 1002 may comprise a photosensitivematerial (e.g., photoresist) formed by a spin coating process.

As shown in the cross-sectional view 1100 of FIG. 11, the masking layer1002 is patterned to re-open the cap cavity 902 and the gate cavity 904.In some embodiments, where the masking layer 1002 comprises aphotosensitive material, the layer of photosensitive material isselectively exposed to electromagnetic radiation according to aphotomask. The electromagnetic radiation modifies a solubility ofexposed regions within the photosensitive material to define solubleregions. The masking layer 1002 (e.g., the photosensitive material) issubsequently developed to define the cap cavity 902 and the gate cavity904 by removing the soluble regions. In some embodiments, the maskinglayer 1002 is patterned such that a portion 1002 p of the masking layer1002 remains between the cap cavity 902 and the gate cavity 904.

As shown in the cross-sectional view 1200 of FIG. 12, a gate electrodematerial 1202 is deposited over the masking layer 1002 and within thecap cavity (902 of FIG. 11) and the gate cavity (904 of FIG. 11). Thegate electrode material 1202 may comprise, in some embodiments, titaniumnitride. In other embodiments, the gate electrode material 1202 maycomprise other conductive materials, such as, for example, nickel,tungsten, titanium, or platinum. The gate electrode material 1202comprises a different material than the source and drain contacts 116,110.

As shown in the cross-sectional view 1300 of FIG. 13, in someembodiments, the gate electrode material 1202 of FIG. 12 may undergo aplanarization process (e.g., chemical mechanical planarization process),to form a cap structure 118 within the cap cavity (902 of FIG. 11) and agate electrode 112 within the gate cavity (904 of FIG. 11). In someembodiments, the cap structure 118, the gate electrode 112, the sourcecontact 116 and the drain contact 110 have top surfaces that aresubstantially co-planar because of the planarization process. In someembodiments, the planarization process is conducted until thepassivation layer 122 is exposed, and thus, the masking layer 1002 maystill remain on portions of the passivation layer 122.

As shown in the cross-sectional view 1400 of FIG. 14, the masking layer(1002 of FIG. 13) is removed. In some embodiments, the masking layer(1002 of FIG. 13) is removed by an etch (e.g., wet or dry) that isselective to the material of the masking layer (1002 of FIG. 13).Together, the steps in FIGS. 13-14 to form the cap structure 118 and thegate electrode 112 may be defined as a second patterning step.

In some embodiments, the cap structure 118 comprises a material (e.g.,the gate electrode material 1202 of FIG. 12) that has a higher workfunction than the active layer 108. Thus, the cap structure 118 acts asa Schottky contact with the active layer 108. In some embodiments, thecap structure 118 directly contacts the active layer 108 and the capstructure 118 does not diffuse into the active layer 108. Thus, in someembodiments, the cap structure 118 comprises a first material and actsas a Schottky contact with the active layer 108, whereas the sourcecontact 116 comprises a second material that is different than the firstmaterial and acts as an Ohmic contact with the active layer 108.Therefore, in some embodiments, cap structure 118, as a Schottkycontact, may increase the resistance in the heterojunction (124 of FIG.1A) and may thereby reduce the saturation current of the HEMT device.

As shown in the cross-sectional view 1500 of FIG. 15, a dielectricmaterial 1302 is deposited over the passivation layer 122. In someembodiments, the dielectric material 1302 may comprise, for example, anitride (e.g., silicon nitride, silicon oxynitride), a carbide (e.g.,silicon carbide), an oxide (e.g., silicon oxide), borosilicate glass(BSG), phosphoric silicate glass (PSG), borophosphosilicate glass(BPSG), a low-k oxide (e.g., a carbon doped oxide, SiCOH), or the like.Thus, in some embodiments, the passivation layer 122 and the dielectricmaterial 1302 may comprise a same material. In other embodiments, thepassivation layer 122 and the dielectric material 1302 may comprisedifferent materials.

As shown in the cross-sectional view 1600 of FIG. 16, the dielectricmaterial 1302 of FIG. 15 is patterned to form a dielectric structure 126that defines contact cavities 1402. The dielectric structure 126 may bepatterned using photolithography and an etch. The contact cavities 1402down from a top surface of the dielectric structure 126 to expose thesource contact 116, the drain contact 110, and the gate electrode 112.

As shown in the cross-sectional view 1700 of FIG. 17, contact vias 120are formed within the contact cavities 1402 of FIG. 16. In someembodiments, the contact vias 120 may be formed by depositing aconductive material over the dielectric structure 126 and performing aplanarization process (e.g., a chemical mechanical planarizationprocess) such that the contact vias 120 have top surfaces that aresubstantially co-planar with a top surface of the dielectric structure126. In some embodiments, the conductive material of the contact vias120 may comprise, for example, copper or tungsten.

FIG. 18 illustrates a flow diagram of a method 1800 of some embodimentsof forming a HEMT device with a cap structure contacting a sourcecontact, thereby corresponding to FIGS. 3-17.

While method 1800 is illustrated and described below as a series of actsor events, it will be appreciated that the illustrated ordering of suchacts or events are not to be interpreted in a limiting sense. Forexample, some acts may occur in different orders and/or concurrentlywith other acts or events apart from those illustrated and/or describedherein. In addition, not all illustrated acts may be required toimplement one or more aspects or embodiments of the description herein.Further, one or more of the acts depicted herein may be carried out inone or more separate acts and/or phases.

At 1802, a passivation layer is deposited over a heterojunctionstructure that is over a substrate. FIG. 6 illustrates a cross-sectionalview 600 of some embodiments corresponding to act 1802.

At 1804, a source contact and a drain contact are formed within thepassivation layer such that the source and drain contacts are laterallyseparated and contact the heterojunction structure. FIGS. 7 and 8illustrate cross-sectional views 700 and 800, respectively, of someembodiments corresponding to act 1804.

At 1806, a first patterning step is performed to remove portions of thepassivation layer to define a first cavity and a second cavity. Thefirst cavity is laterally between the source and drain contacts, and thesecond cavity is laterally between the first cavity and the sourcecontact. FIG. 9A illustrates a cross-sectional view 900A and FIGS. 9Band 9C illustrate a top-views 900B and 900C, respectively, of someembodiments corresponding to act 1806.

At 1808, a gate electrode material is deposited over the first andsecond cavities. FIG. 12 illustrates a cross-sectional view 1200 of someembodiments corresponding to act 1808.

At 1810, a second patterning step is performed to form a gate structurewithin the first cavity and a cap structure within the second cavity.The cap structure is spaced apart from the gate structure by thepassivation layer, and an upper portion of the cap structure directlycontacts the source contact. FIGS. 13 and 14 illustrate cross-sectionalviews 1300 and 1400, respectively, of some embodiments corresponding toact 1810.

Therefore, the present disclosure relates to a method of manufacturing aHEMT device and a corresponding structure of a HEMT device thatcomprises a cap structure contacting a source contact in order todecrease the saturation current and therefore increase reliability ofthe HEMT device during high power applications.

Accordingly, in some embodiments, the present disclosure relates to ahigh voltage device, comprising: a substrate comprising a firstsemiconductor material; a channel layer comprising a secondsemiconductor material over the substrate; an active layer comprising athird semiconductor material over the channel layer; a source contactand a drain contact over the active layer and laterally spaced apartfrom one another; a gate structure laterally between the source contactand the drain contact and arranged over the active layer to define ahigh electron mobility transistor (HEMT) device, the gate structurecomprising a gate electrode; and a cap structure coupled to the sourcecontact and arranged between the gate structure and the source contact,wherein the cap structure is laterally spaced from the gate structure,and wherein the cap structure and the gate electrode comprise the samematerial.

In other embodiments, the present disclosure relates to a high electronmobility transistor (HEMT) device, comprising: a heterojunctionstructure arranged over a semiconductor substrate, the heterojunctionstructure comprising: a binary III/V semiconductor layer to act as achannel layer of the HEMT device, and a ternary III/V semiconductorlayer arranged over the binary III/V semiconductor layer to act as anactive layer; source and drain regions arranged over the heterojunctionstructure and spaced apart from one another in a first direction,wherein the first direction is parallel to an upper surface of thesemiconductor substrate; a gate structure arranged over theheterojunction structure and arranged between the source and drainregions, wherein the gate structure comprises a gate electrode thatcomprises a first material; and a cap structure arranged over theheterojunction structure and directly contacting the source region andthe ternary III/V semiconductor layer, wherein the cap structure isarranged between the source region and the gate structure in the firstdirection, wherein the cap structure is spaced from the gate structure,and wherein the cap structure comprises the first material.

In yet other embodiments, the present disclosure relates to a method offorming high electron mobility transistor (HEMT) device, comprising:depositing a passivation layer over a heterojunction structure over asubstrate; forming a source contact and a drain contact within thepassivation layer, wherein the source contact and the drain contact arelaterally separated from one another and contact the heterojunctionstructure; performing a first patterning step to remove portions of thepassivation layer to define a first cavity and a second cavity in thepassivation layer, wherein the first cavity is laterally between thesource contact and the drain contact, and wherein the second cavity islaterally between the first cavity and the source contact, and whereinthe second cavity is laterally spaced apart from the source contact andthe first cavity by the passivation layer; depositing a gate electrodematerial over the passivation layer and in the first cavity and thesecond cavity; and performing a second patterning step to form a gatestructure within the first cavity and a cap structure within the secondcavity from the gate electrode material, wherein the cap structure isspaced apart from the gate structure by the passivation layer, andwherein an upper portion of the cap structure directly contacts asidewall of the source contact.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A high voltage device, comprising: a substratecomprising a first semiconductor material; a channel layer comprising asecond semiconductor material over the substrate; an active layercomprising a third semiconductor material over the channel layer; asource contact and a drain contact over the active layer and laterallyspaced apart from one another; a gate structure laterally between thesource contact and the drain contact and arranged over the active layerto define a high electron mobility transistor (HEMT) device, the gatestructure comprising a gate electrode; and a cap structure coupled tothe source contact and arranged between the gate structure and thesource contact, wherein the cap structure is laterally spaced from thegate structure, and wherein the cap structure and the gate electrodecomprise the same material.
 2. The high voltage device of claim 1,wherein an upper portion of the cap structure directly contacts an uppersidewall of the source contact, and wherein a bottom portion of the capstructure is laterally spaced from a lower sidewall of the sourcecontact.
 3. The high voltage device of claim 1, wherein the capstructure comprises a different material than the source contact.
 4. Thehigh voltage device of claim 1, wherein the cap structure comprisesmultiple cap segments along a length of the source contact, wherein eachcap segment is spaced apart from its nearest neighboring cap segment bya passivation layer, and wherein each cap segment of the multiple capsegments are substantially aligned with one another.
 5. The high voltagedevice of claim 1, wherein the cap structure continuously extends alonga length of the source contact.
 6. The high voltage device of claim 1,wherein the cap structure is “L-shaped” from a cross-sectional view. 7.The high voltage device of claim 1, wherein the cap structure comprisesa first bottom surface above a second bottom surface, wherein the firstbottom surface is spaced apart from the active layer, and wherein thesecond bottom surface directly contacts the active layer.
 8. The highvoltage device of claim 1, wherein the cap structure is conductive andelectrically coupled to the source contact.
 9. A high electron mobilitytransistor (HEMT) device, comprising: a heterojunction structurearranged over a semiconductor substrate, the heterojunction structurecomprising: a binary III/V semiconductor layer to act as a channel layerof the HEMT device, and a ternary III/V semiconductor layer arrangedover the binary III/V semiconductor layer to act as an active layer;source and drain regions arranged over the heterojunction structure andspaced apart from one another in a first direction, wherein the firstdirection is parallel to an upper surface of the semiconductorsubstrate; a gate structure arranged over the heterojunction structureand arranged between the source and drain regions, wherein the gatestructure comprises a gate electrode that comprises a first material;and a cap structure arranged over the heterojunction structure anddirectly contacting the source region and the ternary III/Vsemiconductor layer, wherein the cap structure is arranged between thesource region and the gate structure in the first direction, wherein thecap structure is spaced from the gate structure, and wherein the capstructure comprises the first material.
 10. The HEMT device of claim 9,wherein the source and drain regions comprise a second material that isdifferent from the first material, and wherein the first material has awork function that is greater than a work function of the secondmaterial.
 11. The HEMT device of claim 9, wherein the gate structure isarranged closer to the source region than the drain region.
 12. The HEMTdevice of claim 9, wherein the cap structure comprises a horizontallyextending portion that directly contacts a sidewall of an upper portionof the source region and a vertically extending portion that is spacedapart from the source region, wherein the vertically extending portionhas an upper region that contacts the horizontally extending portion anda lower surface that directly contacts the ternary III/V semiconductorlayer.
 13. The HEMT device of claim 9, wherein the cap structurecontinuously extends along the source region in a second direction,wherein the second direction is perpendicular to the first direction andis parallel to the upper surface of the semiconductor substrate.
 14. TheHEMT device of claim 9, wherein the cap structure comprises multiple capsegments spaced apart from one another and extending along the sourceregion in a second direction, wherein the second direction isperpendicular to the first direction and is parallel to the uppersurface of the semiconductor substrate.
 15. The HEMT device of claim 14,wherein the multiple cap segments are substantially aligned to oneanother in the second direction.
 16. A method of forming high electronmobility transistor (HEMT) device, comprising: depositing a passivationlayer over a heterojunction structure over a substrate; forming a sourcecontact and a drain contact within the passivation layer, wherein thesource contact and the drain contact are laterally separated from oneanother and contact the heterojunction structure; performing a firstpatterning step to remove portions of the passivation layer to define afirst cavity and a second cavity in the passivation layer, wherein thefirst cavity is laterally between the source contact and the draincontact, and wherein the second cavity is laterally between the firstcavity and the source contact, and wherein the second cavity islaterally spaced apart from the source contact and the first cavity bythe passivation layer; depositing a gate electrode material over thepassivation layer and in the first cavity and the second cavity; andperforming a second patterning step to form a gate structure within thefirst cavity and a cap structure within the second cavity from the gateelectrode material, wherein the cap structure is spaced apart from thegate structure by the passivation layer, and wherein an upper portion ofthe cap structure directly contacts a sidewall of the source contact.17. The method of claim 16, wherein the source contact has a top surfacethat is above a top surface of a first portion of the passivation layerthat directly contacts the source contact, and wherein the first portionof the passivation layer laterally separates a lower portion of the capstructure from the sidewall of the source contact.
 18. The method ofclaim 16, wherein the first cavity is spaced from the source contact bya first distance, and wherein the first cavity is spaced from the draincontact by a second distance greater than the first distance.
 19. Themethod of claim 16, wherein the second patterning step is aplanarization process such that after the second patterning step, thesource contact, the cap structure, the gate structure, and the draincontact have substantially co-planar upper surfaces.
 20. The method ofclaim 16, wherein the second cavity comprises multiple sub-cavitiesextending along a length of the source contact, wherein each sub-cavityof the multiple sub-cavities and is spaced apart from one another by thepassivation layer, and wherein each sub-cavity of the multiplesub-cavities is spaced apart from the source contact by the passivationlayer.